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SCIENCE Chapter 17: Stars and the Solar System
(1) STARS AND THE SOLAR SYSTEM 17 Stars and the SolarSystem • The stars, planets, the Moon and the other objects which we see in the sky are called celestial bodies. The Stars • When we see the dark sky at night, we see many stars shining brighter than the others. • Stars are bodies which emit their own light. • They are also present in the sky during the day time, but they are not visible because of the bright sunlight. • The Sun is also a star. • The star nearest to the Earth is the Sun, which is the source of most of the energy on the Earth. • Stars appear to move from east to west as Earth rotates from west to east. • The Sun, being a star, appears to rise in the east and set in thewest. • The huge distances between the Earth and other celestial bodies are measured in light years. • A light year is the distance covered by light in one year. • The Pole star is situated in the direction of the Earth’s axis, and hence, it does not appear to move. Constellations • The stars which form a group which has a recognisable shape of an identifiable object like an animal or a known object is called a constellation.
(2) STARS AND THE SOLAR SYSTEM 17 • To identify the stars, constellations were given their names many hundreds of years ago. • We use constellations to divide the sky because they move so slowly that in our lifetime, they will always be found in about the same place. • The stars contained in a constellation are not at the same distance. They just appear at the same line of sight. • Orion (appears like a human figure with a belt, often referred to as ‘The Hunter’) ✓ It can be seen in the late evenings during winter. ✓ The belt with three bright stars in a row is usually the easiest part of Orion to spot. ✓ It has seven or eight bright stars. The two brightest are Betelgeuse (shoulder) and Rigel(foot). ✓ The brightest star Sirius is located close to Orion. • Ursa Major (Big Dipper, Great Bear, Saptarshi) ✓ It can be seen at night in the summersky. ✓ It has seven prominent stars and appears like a big ladle or a question mark. ✓ There are three stars in the handle of the ladle and four in its bowl.
(3) STARS AND THE SOLAR SYSTEM 17 Mercury Neptune Venus Uranus Sun Earth Saturn Mars Jupiter • Cassiopeia ✓ Cassiopeia is a prominent constellation in the northern sky. ✓ It is visible during winter in the early part of the night. ✓ It looks like a distorted letter ‘W’ or‘M’. The Solar System • The Sun and the celestial bodies which revolve around it form the Solar System. • The Sun is a major source of heat and light for all the planets in the Solar System. • The Solar System consists of a large number of bodies such as planets, comets, asteroids and meteors. • The gravitational attraction between the Sun and these objects keeps them revolving around it. • Earth is the only planet on which life is known to exist. • There are eight planets which revolve around the Sun.